Well I am looking at buying a used canopy and wondered if there were any tell tale signs of a bad one. Like where to look for stress fracures or something like that. It might be hard to find problems because the only one I am looking for is carpeted.
My truck came with a matching topper (that's what we callem here). The lock would not turn with the key. Most likely from road salt. A new one was only about $20 and they installed it and readjusted the topper too. For $20 it is well worth having that work.
Do some research! A lot of companies went out of buisiness and parts can be hard to come by. I bought a Stockland up in Washington a few years back for $75, had broken rear glass. I went to find a replacement to no avail. I went with a new Leer, there a little pricey new, but can be had for a decent price used if you can find one in your color. I would look at all hinge points in the back, look for any signs of leaks around the windows, push on the roof and listen for "cracking" sounds.